YbGaGe

It sparked interest because one group of researchers reported that it exhibits zero thermal expansion, while being conductive.

[2] However, subsequent measurements by other groups were not able to reproduce those results, but rather found expansion coefficients similar to copper.

Near-zero thermal expansion was observed by Booth et al.

It was found that near-zero thermal expansion (NZTE) in YbGaGe is sensitive to stoichiometry and defect concentration.

However, the near-zero thermal expansion mechanism remains elusive.